Fiber reinforced plastics (FRPs) have been widely used as composite materials in various fields, for example, civil engineering and architectural fields, a transportation field, electronic device fields, aviation and aerospace fields, and the like. The thermosetting resin such as an unsaturated polyester resin, a vinyl ester resin, an epoxy resin, a phenol resin, or the like, or a thermoplastic resin such as polyethylene, polypropylene, an acrylonitrile-butadiene-styrene (ABS) resin, polycarbonate, polyacetal, polyamide, polystyrene, polyphenylene sulfide, or the like has been used as a matrix resin in the FRP, and an inorganic fiber such as a glass fiber, a metal fiber, a ceramics fiber, a carbon fiber, or the like, or an organic fiber such as a natural fiber, a polypropylene fiber, a polyamide fiber, a polyester fiber, a polyacrylate fiber, a polyimide fiber, or the like have been used in various forms as a reinforcement fiber. Among these reinforcement materials, particularly, the glass fiber has been mainly used.
Generally, the FRP includes a resin matrix and a reinforcement material which are made of different materials. For example, a FRP using the inorganic fiber such as the glass fiber or the like, or a FRP using an organic fiber made of a different material from that of the resin matrix may have a disadvantage in recyclability of FRP. Therefore, a FRP including the resin matrix and the reinforcement materials which are made of similar compositions, such as thermosetting or thermoplastic polymer resins, and having excellent recyclability has been developed.
In the related arts, an exemplary method of preparing a FRP including the same resin matrix and reinforcement material, the reinforcement material with a high strength and high elasticity fiber or film made of a thermoplastic resin, or the matrix resin which is the same thermoplastic resin as the reinforcement material can be dissolved in an organic solvent, heated and compacted to form a composite. However, since the method uses the solvent, it may cause an environmental contamination. Therefore, a method being capable of simple and efficient method of preparing a FRP having high strength and excellent recyclability has been demanded without generating a negative environmental influence.
For instance, JP Patent No. 3,130,288B discloses a method of obtaining a stretched isotactic polypropylene fiber having a high strength, low elongation, high Young's modulus, high melting point, and low thermal shrinkage ratio, by stretching a crystalline polypropylene fiber at a high stretch ratio under pressurized saturated steam of 0.20 Mpa or more.
Further, U.S. Pat. No. 8,052,913B discloses a simple and efficient method of preparing a polyolefin resin mold reinforced with a polypropylene-based fiber, which has a high strength and excellent recyclability and can be applied to various uses. Specifically, the method includes compacting step of a ply laminating an unstretched matrix layer having a low melting point as an intermediate layer between stretched polymer reinforcement materials under a specific time, temperature and pressure conditions, and cooling the compacted ply. The compacting process is preferably performed at a pressure of 10 MPa or less, and may be performed using a double belt press, or the like.
The physical properties of the resin composite manufactured by the above-mentioned documents depending on a compaction temperature are shown in FIG. 1.
Further, in the disclosure of U.S. Pat. No. 8,021,592, an assembly composed of two or more stretched webs made of polypropylene having a specific melting point, a recrystallization temperature, and a molecular weight is treated and compacted at elevated temperature and pressure conditions being sufficient to partially melt polypropylene, and cooled at a temperature lower than the recrystallization temperature and an elevated pressure condition, at a cooling rate of 35)° C./minutes or higher. The tensile properties of the composite depending on a cooling condition of the resin composite at the time of compact molding are illustrated in FIG. 2.
In the methods disclosed in above U.S. Pat. Nos. 8,052,913 and 8,021,592, a batch-type heating and compaction method using a hot press is used to prepare a self-reinforced composite, however, the batch-typed and discontinuous methods using hot press equipment may deteriorate productivity.
Therefore, a FRP composed of the same materials of matrix resin and a reinforcement resin and a method of preparing the same for achieving high productivity in a continuous process, have been still required.